The present invention relates to a glue applicator, in particular for applying pressure fed glue in hot liquid form, and to gluing equipment and apparatus incorporating a glue applicator.
With existing kinds of glue applicators for the application of pressure fed glue onto moving articles, problems have arisen in achieving precision in the control of the output flow of the glue. These problems are of particular concern when high speed movement of the articles is desired, as the application of the glue coating to the articles must be interrupted between successive articles and in some cases during application to individual articles. In addition, the control of the glue flow is complicated by the viscous consistency of the glue itself, which requires additional attention to ensure that smearing does not occur.
It is difficult to achieve precise control simply by controlling the feed pressure of the glue, as relief of the pressure, which may for example be provided by compressed air, may not be able to be effected with sufficient abruptness to prevent glue from being applied to undesired locations on or between the articles during a pressure change. Greater precision in control of the glue flow is available from valve control of the feed itself, but the valves employed in existing applicators, for example needle and disc valves, are subject to encrustation by the glue with consequent impairment of their operating efficiency, and special designs of valves less liable to this problem tend to be correspondingly more expensive or difficult to manufacture.
The principal object of the invention is therefore the provision of a glue applicator with an improved valve control of the glue flow to allow accurate metering of applied quantities of glue.
A supplementary object of the invention is to provide an applicator of this kind with an efficient valve control which is of relatively uncomplicated construction and is economical to manufacture.
Another object of the invention is the provision of an applicator adapted to avoid spillage of residual glue quantities after the glue flow has been terminated by the valve control.
Yet another object of the invention is the provision of an applicator of a design lending itself to adaptation to different gluing formats, as in, for example, the application of patterns of glue strips to moving production-line articles.
Yet another object of the invention is the provision of gluing equipment combining such an applicator with a control system for supplying a pressure medium to pressure feed the glue, the system enabling control of the supply of the pressure medium in dependence on the operating condition and characteristics of the equipment.
A further object of the invention is the inclusion of such an applicator in gluing apparatus designed for intermittent high-speed operation, with the application of glue by the applicator being controllable to provide cyclically repeated gluing patterns and being able to be terminated when operation of the apparatus is stopped.